1. Field of the Invention
The present invention relates to a drawing apparatus, and to a drawing method, for forming a desired drawing pattern by directly drawing the pattern on a drawing target surface using a drawing engine equipped with a plurality of drawing devices arranged in the direction of the relative movement of the drawing target surface, wherein the drawing engine is designed so that the design spacing of the thus arranged drawing devices is equal to an integral multiple of a unit pixel spacing in the drawing data.
2. Description of the Related Art
Generally, a wiring pattern on a wiring substrate is formed by exposing the substrate, based on wiring pattern design data, and by developing and printing the desired pattern on the substrate, followed by etching. In the exposure process, a photomask is usually used.
On the other hand, a patterning method based on direct drawing that does not use any photomasks has been proposed in recent years. According to the patterning method based on direct drawing, as corrections for the expansion, shrinkage, distortion, displacement, etc. of the substrate can be made either in advance at the drawing data generation stage or in real time, remarkable improvements can be achieved which include, for example, an improvement of the manufacturing accuracy, an improvement of the manufacturing yield, a reduction of the delivery time, and a reduction of the manufacturing cost.
Examples of the patterning method based on direct drawing include a method that forms an exposure pattern by a direct exposure process using a Digital Micromirror Device (DMD) or an electron beam exposure apparatus or the like, and a method that directly forms a wiring pattern by using an inkjet drawing apparatus equipped with an inkjet head. Among these methods, a typical example of the patterning method, based on direct exposure that uses a DMD, is disclosed in the prior art and, for example, in Japanese Unexamined Patent Publication No. 10-112579. According to the technique disclosed therein, when exposing the resist formed on a substrate, pattern data corresponding to the pattern to be exposed is generated, and this pattern data is input to the Digital Micromirror Device (DMD) to cause each of the micromirrors arranged thereon to tilt according to the pattern data, after which light is projected onto the DMD and the reflected light from the micromirrors is directed to the resist to expose it in a pattern that matches the pattern data.
FIG. 16 is a diagram schematically showing a direct drawing system. It is to be understood that, throughout the drawings given hereinafter, component elements designated by the same reference numerals are the component elements having the same functions.
The direct drawing system 100 comprises a drawing apparatus 101 and a computer 102 connected to the drawing apparatus 101. The computer 102 supplies drawing data to the drawing apparatus 101 and controls the drawing apparatus 101. The drawing apparatus 101 comprises a stage 110 on which a drawing target substrate 151 is mounted, and a drawing means 111 which moves in relative fashion over the surface of the drawing target substrate 151 in a direction indicated by an arrow in the figure. The drawing means 111 is equipped with one or more drawing engines (not shown) which are each assigned a drawing area on the surface of the drawing target substrate 151, and which perform drawing operations in parallel. A drawing engine comprises a plurality of drawing heads arranged in rows at prescribed spacing along the direction of the relative movement of the drawing target surface, and the rows of such drawing heads are arranged in a plurality of columns. Here, in the case of a maskless exposure apparatus, the drawing heads of the drawing means 111 are exposure heads for modulating light sources, and in the case of an inkjet drawing apparatus, the drawing heads are inkjet heads that eject ink.
FIG. 17 is a diagram showing the operating principle of the drawing apparatus.
The drawing means 111, which moves in relative fashion over the surface of the drawing target substrate 151, is equipped with a plurality of drawing engines #1 to #N (reference numeral 30) (N is a natural number) arranged in a direction orthogonal to the direction of the relative movement of the drawing target substrate 151. When the drawing target substrate 151 moves relative to the drawing engines #1 to #N at speed Vex, a stage controller 29 generates a signal synchronized to the relative movement (hereinafter called the “synchronizing signal”) and supplies it to each of the drawing engines #1 to #N (reference numeral 30).
The drawing target substrate 151 is divided in a virtual manner into N areas called the “strips #1 to #N” (reference numeral 32). The drawing engines #1 to #N (reference numeral 30), while moving relative to the drawing target substrate 151 at speed Vex, perform drawing on their respective corresponding strips #1 to #N (reference numeral 32). Here, the length of the drawing target substrate 151 in the direction of the relative movement, that is, the length of each of the strips #1 to #N, is denoted by L (hereinafter referred to as the “strip length”).
The area that each of the drawing engines #1 to #N (reference numeral 30) can draw at a time is limited, and the length of the area in the direction of the relative movement of the drawing target substrate 151 is shorter than the strip length L. Therefore, each of the strips #1 to #N (reference numeral 32) is subdivided in a virtual manner into M drawing blocks (i, j) (reference numeral 33) (here, M is a natural number, while 1≦i≦N and 1≦j≦M). When the length of each drawing block (i, j) in the direction of the relative movement is denoted by ΔY, the relation L=M×ΔY holds between the strip length L and the length ΔY of each drawing block (i, j) in the direction of the relative movement. The length of each drawing block (i, j) in the direction orthogonal to the direction of the relative movement of the drawing target substrate 151 is equal to the width of each of the strips #1 to #N (reference numeral 32).
The drawing data is typically bitmap data. As bitmap data requires a huge amount of data for storage, generating and storing the bitmap data prior to drawing would not be preferable as it would consume a large amount of memory resources. Therefore, to conserve the memory resources, for each of the drawing engines #1 to #N (reference numeral 30) the drawing data in bitmap form is generated based on design data in real time during the drawing process by dividing the data in a virtual manner for each of the drawing engines #1 to #N (reference numeral 30), that is, for each of the strips #1 to #N (reference numeral 32), and for each drawing block (i, j) in each of the strips #1 to #N (reference numeral 32); the thus generated data is first temporarily stored in memory, and then sequentially supplied to each corresponding one of the drawing engines #1 to #N (reference numeral 30). Accordingly, each of the drawing engines #1 to #N (reference numeral 30) performs the direct drawing based on the drawing data of bitmap form supplied for each drawing block (i, j). The series of these operations is performed based on the synchronizing signal that the stage controller 29 supplies as the reference signal to each of the drawing engines #1 to #N (reference numeral 30).
FIG. 18 is a flowchart showing the data processing flow in the drawing apparatus.
As shown in FIG. 18, first, the design data 51 is converted into intermediate data 52 in a first data conversion step S101. As the size of the intermediate data 52 is small compared to the size of the bitmap data to be described later, and as the first data conversion step S101 need not be performed in real time during the drawing process, the intermediate data 52 may be generated in advance and stored in memory.
In step S102, the intermediate data for one drawing block is read. Next, an alignment/correction step S103 is performed on the intermediate data thus read for one drawing block, and bitmap data 53 is generated in step S104 and temporarily stored in memory. In step S105, the generated bitmap data 53 is supplied to the corresponding drawing engine in synchronism with the synchronizing signal. In the present specification, the realtime process performed in the above steps S102 to S105 is collectively referred to as the “second data conversion process.” Using the bitmap data 53 supplied for each drawing block through the second data conversion process, the drawing engine performs the direct drawing in step S106. When the drawing on the one drawing block by the drawing engine is completed, the process returns to step S102, where the second data conversion process is performed to obtain the bitmap data 53 for the next drawing block. To describe the above series of processing in another way, the drawing engine in step S106 can be regarded as “consuming” at a constant speed the bitmap data 53 supplied through the second data conversion process in synchronism with the synchronizing signal generated by the stage controller 29.
Taking a maskless exposure apparatus (direct exposure apparatus) as an example of the drawing apparatus, a brief description will be given below of the relationship between the drawing data of bitmap form and the light sources constituting the exposure head. For example, in the case of the patterning method based on direct exposure that uses the DMD as the exposure head, each micromirror corresponds to the light source.
FIG. 19 is a schematic diagram illustrating the concept of the drawing data of bitmap form used in the direct exposure process by the exposure apparatus.
The drawing data is bitmap data composed of pixels arranged in a matrix of n rows and m columns (n and m are integers) as shown schematically in FIG. 19. The coordinates of each pixel in the bitmap data are represented by g(r, c). Here, r indicates the row number in the bitmap data (0≦r≦n−1, where r is an integer), and c indicates the column number in the bitmap data (0≦c≦m−1, where c is an integer). The resolution, i.e., pixel spacing (hereinafter called the “unit pixel spacing”), of the bitmap data is denoted by b. It can be said that the schematic drawing of the bitmap data illustrated in FIG. 19 directly represents the exposure pattern formed (or to be formed) on the surface of the exposure target substrate (drawing target substrate) mounted on the stage (not shown).
FIG. 20 is a schematic diagram illustrating the arrangement of light sources in one drawing engine that performs the direct drawing using the drawing data shown in FIG. 19. Open circles in the figure indicate the light sources forming the exposure head.
The drawing engine that uses bitmap data such as shown in FIG. 19 usually has light sources arranged in a two-dimensional array as shown in FIG. 20.
The light sources are arranged in corresponding relationship to the bitmap data of FIG. 19; that is, m light sources per row are arranged in the column direction, and the spacing of the light sources is equal to b which is the same as the resolution (i.e., the unit pixel spacing) of the bitmap data. The column number c of the bitmap data directly corresponds to the column number c of the light source in the exposure head.
As for the light source arrangement in the row direction, the drawing head is designed so that the spacing D between the two consecutive rows is equal to p times (p is an integer) the unit pixel spacing b in the bitmap data, that is, D=pb. Here, k light sources per column are arranged in the row direction, and the row number is represented by R (0≦R≦b−1, where R is an integer).
The exposure target substrate mounted on the stage (not shown) moves relative to the drawing engine (i.e., the light sources) at a constant speed in a prescribed direction. It can be said that the bitmap data shown in FIG. 19 also moves in a virtual manner relative to the drawing engine (i.e., the light sources) shown in FIG. 20. This virtual relative movement of the bitmap data is accomplished by supplying the necessary bitmap data to the drawing engine in synchronism with the synchronizing signal that the stage controller supplies as the reference signal.
FIGS. 21 to 24 are schematic diagrams for explaining the relationship between the bitmap data shown in FIG. 19 and the light source arrangement in the drawing engine shown in FIG. 20. As described above, the bitmap data schematically shown in each figure corresponds to the exposure pattern formed (or to be formed) on the surface of the exposure target substrate mounted on the stage (not shown). Here, consider the case where the exposure target substrate moves at speed Vex relative to the light sources R in a virtual manner in a direction indicated by an arrow in the figure. In the figure, to simplify the illustration, only some of the light sources in the third column are shown, and the other light sources are not shown.
First, as the initial condition, consider the case where the light source R=0 is aligned with the pixel g(0, 3) in the bitmap data, as shown in FIG. 21. In this condition, the synchronizing signal is sent to the drawing engine, causing the light source R=0 to emit light and thus exposing the pixel g(0, 3).
When, from the initial position, the exposure target substrate mounted on the stage moves relative to the light source by a distance corresponding to the resolution (i.e., the unit pixel spacing) b of the bitmap data (FIG. 22), the synchronizing signal is again sent to the drawing engine. At this time, the pixel g(1, 3) comes into alignment with the light source R=0, and the pixel can thus be exposed. As the light source spacing D (=pb, where p is an integer) is sufficiently larger than the resolution b of the bitmap, the pixel g(0, 3) in FIG. 22 is not aligned with any light source, and is therefore not exposed.
When the exposure target substrate mounted on the stage further moves relative to the light source by the distance b (FIG. 23), the synchronizing signal is again sent to the drawing engine. At this time, the pixel g(2, 3) comes into alignment with the light source R=0, and the pixel can thus be exposed. On the other hand, at this time, the pixels g(0, 3) and g(1, 3) are not aligned with any light source, and are therefore not exposed.
When the exposure target substrate mounted on the stage further moves relative to the light source by the distance b (FIG. 24), the synchronizing signal is again sent to the drawing engine. At this time, the pixel g(3, 3) comes into alignment with the light source R=0, while the pixel g(0, 3) comes into alignment with the light source R=1; as a result, these pixels can be exposed. On the other hand, at this time, the pixels g(1, 3) and g(2, 3) are not aligned with any light source, and are therefore not exposed.
Thereafter, each time the exposure target substrate mounted on the stage moves relative to the light source by the distance b, the synchronizing signal is sent to the drawing engine, and any pixel that comes into alignment with the light source can be exposed. For example, in the case of the pixel g(0, 3), when the exposure target substrate mounted on the stage moves in relative fashion by the distance pb from the initial position, the pixel comes into alignment with the light source R=1, and the pixel can thus be exposed one more time. In the case of the pixel g(1, 3), for example, when the exposure target substrate mounted on the stage moves in relative fashion by the distance (p+1)b from the initial position, the pixel comes into alignment with the light source R=1, and the pixel can thus be exposed one more time.
In this way, as the exposure target substrate moves in relative fashion below the drawing engine having k light sources in each column, each pixel in the bitmap data is exposed to light a total of k times. In the direct exposure apparatus, whether the intended exposure process is completed or not is determined by whether the light energy accumulated through k exposures exceeds the threshold of the photosensitive material applied on the exposure target substrate. Accordingly, if the number, k, of light sources is sufficiently large, then even if some of the k light sources fail to emit light properly due, for example, to the failure of driving transistors in the LCD or of micromirrors in the DMD in the patterning method using the DMD, the possibility that such failure will have a serious effect on the final exposure result is small. Stated another way, such redundancy in the number of light sources constitutes the basis for the reliability of the above-described exposure apparatus.
The operation of the drawing apparatus described above holds good only when the drawing engine is manufactured by strictly satisfying various design requirements. In reality, however, due to variations in hardware manufacturing, it is difficult to strictly satisfy these design requirements.
For example, in the case of the drawing data of bitmap form, as the data is generated by software on the externally connected computer, it is relatively easy to achieve the required data resolution b. On the other hand, the design condition requires that the light source spacing D in the exposure head be strictly equal to an integral multiple of (i.e., p times) the resolution (i.e., the unit pixel spacing) b of the bitmap data, but it is extremely difficult to strictly satisfy this design requirement in actual hardware because its mechanical construction is complicated. For example, when the drawing apparatus is a direct exposure apparatus, it is difficult to achieve the light source spacing as designed by finely adjusting the optics of the light sources mounted in the drawing engine. Accordingly, the light source spacing E in the exposure head actually manufactured with reference to the design (ideal) light source spacing D in the exposure head will end up being different from the design spacing D (i.e., E≠D). As a result, the value “a”(=E/p), obtained by dividing the actual spacing E by the integer p, becomes different from the unit pixel spacing b of the bitmap data (i.e., the resolution of the bitmap data). In the present specification, “a” will be referred to as the “actual pixel spacing.” To summarize the above discussion, the following two relations can be obtained, where δ is the displacement.
                                                                                                                                a                    -                    b                                                                    ≤                δ                                                                                                                                                D                    -                    E                                                                    ≤                                  p                  ⁢                                                                          ⁢                  δ                                                                    }                            (        1        )            
If direct drawing such as described above is performed without correcting the displacement δ, that is, in the condition of a≠b, the following problem occurs. Suppose that, for a given pixel, the drawing position becomes displaced by δ from the correct position per each drawing operation. As the drawing operation is performed k times, this displacement builds up, and a displacement of the order of k×pδ at maximum can result. As a result, the intended resolution performance cannot be obtained. For example, in the case of the exposure apparatus, the exposure pattern blurs. As one drawing apparatus is usually equipped with a plurality of drawing engines, and as the displacement δ differs from one drawing engine to another, it follows that the resolution performance varies among the drawing engines.
In view of the above problem, it is an object of the present invention to provide a drawing apparatus and a drawing method that can efficiently perform stable drawing operations while maintaining a high resolution performance, as intended, when drawing a desired drawing pattern, by drawing the pattern directly on a drawing target surface using a drawing engine equipped with a plurality of drawing heads arranged along the direction of the relative movement of the drawing target surface, the drawing engine being designed so that the design spacing of the thus arranged drawing heads is equal to an integral multiple of a unit pixel spacing in drawing data.